Optimization of sample unit's shape and size to enhancing precision and accuracy of density estimation of Astragalus verus in Mayan rangeland, Mashhad

Because plant density is often measured by using plots and also in most cases are done by the method of estimation and counting the individuals، so one of the important cases that we have to decide on is the size and shape of plot. In this research، the density of Astragalus verus that it''s one of the dominate species in the area and has separate and recognizable individuals plant from each other،for investigate the effects of different size and shape of plots on sampling precision and accuracy are estimated in Mayan Mashhad area. The shapes of plot are square، wide rectangular، long rectangular، and sizes of plot are 1، 2، 4، and 8 m2 respectively، that we have been investigated in total 3x4 plots (treatments). In this research، the coordinates of individual plants and the boundary of study area are located by using digital camera. Then، with help of R software، the digital map of study area was sketched. The results show that long rectangular 0. 5x4 m plot has the highest accuracy and precision، so it is selected as optimum plot. Finally، it can be concluded that for saving time and expenses in sampling، using of locating coordinates method of individual plants and application of R software can be appropriate approach for estimating the density of shrublands، so for similar shrublands، the optimum plot of this research (4x0. 5 m) can be used.